Relationship between rainfall and sheep farm productivity : case studies in a variable environment

Abstract

Relationships between quantity of rainfall, reproductive and wool performance were examined for at least the last decade on four properties situated in the East Coast dryland environment. Results from all properties varied. The overall effect rainfall showed to have on wool production was significant. Case study one (for which two lagged observations proved significant) showed 79.6% of the variation in total wool production and 48.4% of wool/SU were attributed to rainfall one year prior. Inverse correlations (refer to Appendix 7) with a one and two year lag in both total wool and wool/SU observed with case study four (for which all lagged observations proved significant), indicate the management policies imposed on the property to reduce competition to capital breeding stock, therefore increasing total wool production. Overall wool production is attributed to liveweight and Kelly et al (1983 concluded "there is an association of 0.1 kg greasy wool per 1 kg liveweight" (Hawker, unpublished). Rainfall also showed to have a significant effect on lamb production. Case study one (for which only one lagged observation proved significant) showed 47.6% of the difference in lamb production is attributed to rainfall one year prior. This is once again due to liveweight and liveweight change, therefore influencing ovulation rate and litter size. Case study four (for which two lagged observations proved significant), once again showed inverse correlations (refer to Appendix 7) due to the management policies discussed earlier. Kelly and Johnstone (1982) concluded, "if ovulation rate is converted to lambs born using an average correction factor of 0.65, a 1 kg increase in mean liveweight at joining is associated with an increase of 2 lambs born per 100 ewes lambing." Therefore to maximise wool production and ovulation rate, ewe liveweights should be kept as high as possible over summer-autumn. This is affected by rainfall, its influence on pasture production and nutrition.